A Generalized Theory of Particulate Electron Conduction Enzymes Applied to Cytochrome Oxidase. A Theory of Coupled Electron and/or Iron Transport Applied to Pyruvate Carboxylase

摘要

A previously developed theory of particulate electron conduction enzymes was based on a model of an enzyme particle catalyzing the oxidation-reduction of two different substrates at two different enzymatic sites on the same particle with conduction of electrons between the two sites through the enzyme particle. Using the simplifying assumption that the per cent reduction of the second substrate is held constant, there was previously shown to be a hyperbolic relationship between the first order rate constant (k') and the sum (C sub x) of oxidized plus reduced substrate, of the form k'=alpha/(C sub x + beta), where alpha and beta are positive constants. It is shown here that if this simplifying assumption is omitted, a positive constant is added to the right hand side of this equation, which describes exactly the experimental data of Smith and Conrad on cytochrome oxidase. If electron transport is assumed to be coupled to ion transport, this equation becomes k'=(alpha/C sub x)-gamma (where gamma is a positive constant) which describes the experimental data of Eadie and Gale on pyruvic carboxylase of yeast. It seems probable that the same theory is applicable to coupled ion-ion transport and coupled electron-electron transport in both membranous systems, and in particulate preparations consisting of membrane fragments. (Author)